This invention relates to resist compositions for high resolution electron beam lithography. More particularly, it is concerned with electron beam resist compositions, media for electron beam lithography, and a method for electron beam lithography, all based upon ionic polymers.
Photolithography has been employed for some time in the electronics industry for the production of circuit patterns. In known processes, a layer of resist material is applied to the substrate and patterned by exposure to light through a mask which defines the desired pattern. Upon exposure to light, the photoresist changes solubility, becoming either more soluble (positive working resist) or less soluble (negative working resist) in the developer solvent.
Most known positive working resists are polymeric materials which undergo a degradative reaction upon exposure to yield products which are more soluble in the developer solvent. Because most positive working resists function by this mechanism, they tend to be less sensitive than negative working resists. Negative resists generally function by a mechanism involving a radiation-induced increase in molecular weight, usually as a result of cross-linking, to produce a change in solubility. Negative working resists are generally preferred because of their greater sensitivity, but often exhibit undesirable swelling upon development due to cross-linking and entrapment of solvent in the cross-linked polymer net. Swelling can be a serious problem in applications which require high resolution.
In the production of integrated electronic circuit devices by microlithography, designs trends are toward increasing the scale of device complexity, and hence the density of circuit patterns, to reduce fabrication costs and increases performance. This goal imposes a number of requirements upon lithographic resist materials employed in the manufacture of such devices, notably resolution, sensitivity and etch resistance.
With increasing miniaturization of circuit patterns, the limit of usefulness of optical means for exposure imposed by unwanted diffraction effects is rapidly being approached. Electron beam lithography recently has found increased use in the production of microcircuit devices. Electron beams, by virtue of their shorter effective wavelength and increased depth of focus, can record information at higher densities and resolution than can light beams. The increasing use of electron beam lithography has spurred recent interest in the search for suitable electron beam resist materials. While some photoresist materials can also be used for electron beam lithograph, most cannot. Moreover, since many known electron beam resists are positive working and do not have the sensitivity or etch resistance of negative working resists, the latter are preferred.